Rectangle with rounded ends

Newer versions directly support rounding the ends of rectangles:

see: https://carbide3d.com/carbidecreate/unstable/ and

https://carbide3d.com/blog/2019/carbide-create-400/

To do it with Boolean operations, see:

https://docs.carbide3d.com/assembly/carbidecreate/video-tutorials/#boolean-operations

and